CO2 laser

ABSTRACT

Efficient laser diode excited Thulium (Tm) doped solid state systems, directly matched to a combination band pump transition of Carbon Dioxide (CO 2 ), have matured to the point that utilization of such in combination with CO 2  admits effectively a laser diode pumped CO 2  laser. The laser diode excited Tm solid state pump permits Continuous Wave (CW) or pulsed energy application. Appropriate optical pumping admits catalyzer free near indefinite gas lifetime courtesy of the absence of significant discharge driven dissociation and contamination. As a direct consequence of the preceding arbitrary multi isotopologue CO 2 , symmetric and asymmetric, gas mixes may be utilized without significant degradation or departure from initial mix specifications. This would admit, at raised pressure, a system continuously tunable from ˜9 μm to ˜11.5 μm, or sub picosecond amplification. This methodology offers advantages in regards scalability, pulse energy and power over alternative non linear conversion techniques in access to this spectral region.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates to high power, infra-red, optically pumped CO₂lasers.

2. Description of the Prior Art

U.S. Pat. No. 3,810,042 (Tunable Infrared Molecular Laser OpticallyPumped by a Hydrogen Bromide Laser) describes lasers that are disclosed,wherein there are laser configurations in which a high pressuremolecular medium such as compressed CO2, liquid CO2 or solid CO2 ispumped by a hydrogen-bromide molecular laser. The hydrogen-bromidelaser, when transversely excited, can provide high pump powers between4.0 and 4.6 micrometers wavelength. This wavelength range is desirablefor pumping molecules having a linear three-atomic skeletal, includingthose molecules which are simple linear three-atomic molecules. Anexample of a more complicated molecule having a linear three-atomicskeletal is CH2CO. The active medium has a spectrum ofvibrational-rotational emission lines that merge into a continuum thatis suitable for mode-locked pulsing or tunable operation.

The primary deficiency is the use of a Hydrogen Bromide (HBr) lasermolecular pump which, in practice, is not suitable. Chemical lasers,though in general efficient, require the handling of exhaust product andprecursor fuel and oxidizer. Even if purely cold-reaction dischargeinitiated by dissociation of a halogen donor, these are then typicallyinefficient and still require product gas handling. In addition, HBr isa multiline molecular laser with a defined emission line structure, thusat approximately atmospheric pressure or less, the Carbon Dioxide (CO₂)attributable absorption line structure is only in sporadic proximity toa limited number of HBr lines, both CO₂ and HBr of limited bandwidth,and thus efficient pump utilization is not easily achieved under suchconditions. That is to say, HBr is not continuously tunable within abroad band, thus as a pump for CO₂ it offers, at low to moderatepressure, no more than ,limited line matching. In addition, the 1→0vibrational transition of HBr occupies the spectral range 2400 cm⁻¹ to2700 cm⁻¹, which presents essentially no spectral overlap with the00⁰0→00⁰1 CO₂ transition being pumped. The forgoing has directimplications in regards baseline useful emission, for any isotopologueof CO₂, from HBr, and thus global system efficiency whether or not CO₂is at pressure. Further deficiencies, common to this cited prior art andthose cited below are presented in the final paragraphs of this section.

U.S. Pat. No. 3,860,884 (Optically Pumped N₂O or similar gas mixed withEnergy Transferring CO₂) describes a powerful excitation technique for amixture of molecular gases in which a combination of optical pumping andresonant energy transfer is used. An optically-pumped N₂O laser pumpedat 4.3 μm by HBr laser is “seeded” with a minor portion of CO₂, whichabsorbs the pumping radiation and transfers it by vibration-vibrationenergy transfer to invert the populations of the 00⁰1 and 10° levels ofthe N₂O. In this laser oscillations have been achieved at 10.5 μm attotal pressure up to 42 atmospheres, which is more than an order ofmagnitude greater than feasible in an optically-pumped N₂O laser withoutCO₂. The advantages of broad tunability and short pulse width areobtainable. In addition, a rare isotope CO₂ laser employs ¹³C¹⁶O₂ tocomprise at least 90 percent and possibly as much as 97 percent of thegas mixture, together with as little as 3 percent of ordinary CO₂(¹²C¹⁶O₂). Only the ordinary CO₂ absorbs a significant portion of thepumping radiation directly; but significant energy transfer occurs bycollision from the ordinary CO₂ to the ¹³C¹⁶O₂. Laser oscillation isthereby obtainable between about 9 μm and 11 μm for a total pressureexceeding about 40 atmospheres.

The primary deficiency is, as per the prior cited patent, the use of aHydrogen Bromide (HBr) laser pump which, in practice, is not suitable.Chemical lasers, though in general efficient, require the handling ofexhaust product and precursor fuel and oxidizer. Even if purelycold-reaction discharge initiated by dissociation of a halogen donor,these are then typically inefficient and still require product gashandling. In addition, the 1→0 transition of HBr occupies the spectralrange 2400 cm⁻¹ to 2700 cm⁻¹, which presents essentially no spectraloverlap with the 00⁰0→00⁰1 CO₂ transition being pumped, for anyisotopologue of CO₂. The forgoing has direct implications in regardsbaseline useful emission from HBr, and thus global system efficiencywhether or not CO₂ is at pressure. Further deficiencies, common to thiscited prior art and those cited below are presented in the finalparagraphs of this section.

U.S. Pat. N. 4,145,668 (Optically Resonance Pumped Transfer Laser withHigh Multiline Photon to Single Line Photon conversion efficiency)describes lasers that are disclosed, wherein trapped multiline laserradiation from a DF laser is employed to pump a DF+CO₂ working gasmixture within the optical resonator for the DF laser. The multilinepumping energy is resonantly absorbed by the DF component of the workinggas mixture and collisionally transferred to upper energy levels oflasing transitions in CO₂. A narrow-band optical resonator disposedabout the working gas interaction region with the pumping radiation andtuned to a desired CO₂ transition enables a single line laser output tobe obtained on the desired transition.

The primary deficiency is, as per the prior cited patents, the use of achemical laser pump which, in practice, is not suitable. In this case,the specified Deuterium Fluoride (DF) laser pump is not practical.Chemical lasers, though in general efficient, require the handling ofexhaust product and precursor fuel and oxidizer. Even if purelycold-reaction discharge initiated by dissociation of a halogen donor,these are then typically inefficient and still require product gashandling. Further deficiencies, common to this cited prior art and thosecited below are presented in the final paragraphs of this section.

The article, New Direct Optical Pump Schemes for Multi-atmosphere CO₂and N₂O Lasers [K. Stenersen et al, IEEE Journal of Quantum Electronics,25(2), 1989, 147-153] describes nine schemes for direct optical pumpingof multi-atmosphere CO₂ and N₂O lasers at pump wavelengths in the1.4-3.6 μm region. Most of these wavelengths can be generated bysolid-state lasers, which are more attractive pump sources than thechemical lasers (HBr, HF) used previously to pump high-pressure CO₂ andN₂O lasers. Including previously studied pump schemes, there arealtogether 14 possible pump transitions in CO₂ and N₂O in the 1.4-4.5 μmregion. Numerical laser simulations are carried out to compare all ofthese pump schemes. Assuming 10 J/cm² pump energy in a pulse of 100 nsFWHM, and 5% output coupling as the only resonator loss, the calculatedenergy conversion efficiencies are in the range of 6-40%. The pumpthresholds are in the range of 0.1-3.1 J/cm².

This article correctly identifies the 00 ⁰ 0→20 ⁰ 1 transition as apossible CO₂ optical pump path but it is deficient in that relatedidentified solid state (Co:MgF₂, Er:YLF) optical pump systems are simplynot sensible. At room temperature the Co:MgF₂ upper state lifetime is˜35 μs. Thus Co:MgF₂ can only be pumped, at room temperature, by anotherpulsed laser, perhaps laser diode excited. Global efficiency willdiminish for each new laser inserted in the system chain, as willcomplexity, thus an undesirable concept. To date, Nd:YAG at 1338 nm hasbeen used to pump Co:MgF₂, and Nd:YAG on this line is no more than ˜24%efficient, and pumped Co:MgF₂ was no more than ˜35% efficient to yield anet best pump source efficiency of ˜8%. Since the primary laser diodespumping Nd:YAG would be ˜55% efficient the optical to electricalefficiency of this pump system would be ˜5%. This as opposed to the ˜25%or better feasible for the laser diode pumped Tm:YAG for example. In thecase of Er lasers, they simply cannot efficiently get into the correctpump band around ˜2 um for CO₂. The article is deficient in that it doesnot identify the 01¹1 level as a possible, beneficial, metastable levelderiving from the identified pump transition. Other deficiencies arepresented in the final paragraphs of this section.

The article, Direct Optically Pumped Multiwavelength CO₂ Laser [M. I.Buchwald et al, Applied Physics Letters, 29(5), 1976, 300-302] describesan HF laser that was used to directly pump various isotopic forms ofCO₂. Intense laser emission was observed on numerous lines in the 4.3,10.6, and 17 μm regions. All observed 4.3 and 17 μm CO₂ laser emissionlines were assigned. The pressure dependence of lasing spectra and laserpulse temporal features were examined.

This approach is deficient in that optical pumping of CO₂ on the00⁰0→10⁰1 transition was employed. This required a Hydrogen Fluoride(HF) laser which is not sensible from a practical standpoint. As per theprior cited patents, the use of a chemical laser pump, which inpractice, is not suitable. In this case, the specified Hydrogen Fluoridelaser pump is not practical. Chemical lasers, though in generalefficient, require the handling of exhaust product and precursor fueland oxidizer. Even if purely cold-reaction discharge initiated bydissociation of a halogen donor, these are then typically inefficientand still require product gas handling. In addition, it is of course amultiline laser and there is only coincidental approximate line matchingof some form and the transition offers no meaningful spectral overlapwith the 00⁰0→10⁰1 pump transition. All of which has direct implicationsin terms of net efficiency and suitability as a pump for molecular CO₂.Further deficiencies, common to this cited prior art and those citedbelow are presented in the final paragraphs of this section.

The article, Optically Pumped Atmospheric Pressure CO₂ Laser [T. Y.Chang et al, Applied Physics Letters, 21, 1972, 19] describes laseraction at 10.6 μm that has been obtained in pure CO₂ gas at pressures upto 1 atm by optically pumping with the 4.23 μm line of a TEA HBr laser.The potential usefulness of this method for pumping very high densityCO₂ is discussed.

The primary deficiency is, as per the prior cited patents and article,the use of a Hydrogen Bromide laser pump which, in practice, is notsuitable. HBr is a multiline molecular laser with a defined emissionline structure, thus at approximately atmospheric pressure or less theCO₂ attributable absorption line structure is only in sporadic proximityto a limited number of HBr lines, both CO₂ and HBr of limited bandwidthand thus efficient pump utilization is not easily achieved under suchconditions. That is to say, HBr is not continuously tunable within abroad band, thus as a pump for CO₂ it offers, at low to moderatepressure, no more than limited line matching. In addition, the 1→0transition of HBr occupies the spectral range 2400 cm⁻¹ to 2700 cm⁻¹,which presents essentially no spectral overlap with the 00⁰0→00⁰1 CO₂transition being pumped. The forgoing has direct implications in regardsbaseline useful (for any isotopologue of CO₂) emission from HBr, andthus global system efficiency whether or not CO₂ is at pressure.Furthermore chemical lasers, though in general efficient, require thehandling of exhaust product and precursor fuel and oxidizer. Even ifpurely cold-reaction discharge initiated by dissociation of a halogendonor, these are then typically inefficient and still require productgas handling. Further deficiencies, common to this cited prior art andthose cited below are presented in the final paragraphs of this section.

The article, Optically Pumped N₂O Laser [T. Y. Chang et al, AppliedPhysics Letters, 22, 1973, 93], describes laser action at 10.8 μm thathas been obtained in pure N₂O gas at pressures up to 270 Torr byoptically pumping with the 4.465 μm line of a TEA HBr laser. Possibleextension of this pumping technique to other linear three-atomicmolecules and molecules with a linear three-atomic skeletal isdiscussed.

The primary deficiency is, as per the prior cited patents and articles,the use of a Hydrogen Bromide laser pump which, in practice, is notsuitable. Chemical lasers, though in general efficient, require thehandling of exhaust product and precursor fuel and oxidizer. Even ifpurely cold-reaction discharge initiated by dissociation of a halogendonor, these are then typically inefficient and still require productgas handling. In addition, HBr is a multiline molecular laser with adefined emission line structure, thus at approximately atmosphericpressure or less the N₂O attributable absorption line structure is onlyin sporadic proximity to a limited number of HBr lines, both N₂O and HBrof limited bandwidth and thus efficient pump utilization is not easilyachieved under such conditions. That is to say, HBr is not continuouslytunable within a broad band, thus as a pump for N₂O it offers, at low tomoderate pressure, no more than limited line matching. In addition, the1→0 transition of HBr occupies the spectral range 2400 cm⁻¹ to 2700cm⁻¹, which presents essentially no spectral overlap with the 00⁰0→00⁰1N₂O transition being pumped. The forgoing has direct implications inregards baseline useful emission from HBr, and thus global systemefficiency whether or not N₂O is at pressure. Further deficiencies,common to this cited prior art and those cited below are presented inthe final paragraphs of this section.

The article, Optically Pumped 33 atm CO₂ Laser [T. Y. Chang et al, 23,1973, 370], describes single nanosecond laser pulses at wavelengths near10 μm that have been obtained by using a pulsed HBr laser to opticallypump pure CO₂ gas at pressures up to 33 atm in a 1 mm-long opticalresonator. At pressures above 17 atm, the laser oscillates on the 10.3μm R branch rather than on the usual 10.6 μm P branch.

The primary deficiency is, as per the prior cited patents and article,the use of a Hydrogen Bromide laser pump which, in practice, is notsuitable. Chemical lasers, though in general efficient, require thehandling of exhaust product and precursor fuel and oxidizer. Even ifpurely cold-reaction discharge initiated by dissociation of a halogendonor, these are then typically inefficient and still require productgas handling. In addition, the 1→0 transition of HBr occupies thespectral range 2400 cm⁻¹ to 2700 cm⁻¹, which presents essentially nospectral overlap with the 00⁰0→00⁰1 CO₂ transition being pumped. Theforgoing has direct implications in regards baseline useful (for anyisotopologue of CO₂) emission from HBr, and thus global systemefficiency whether or not CO₂ is at pressure. Further deficiencies,common to this cited prior art and those cited below are presented inthe final paragraphs of this section.

The article, Optically Pumped 16 μm Laser [R. M. Osgood, Applied PhysicsLetters, 28, 1976, 342] describes a potentially useful 16 μm CO₂ laser,oscillating on the [10°0,02°0] to 01¹0 transition, is described. Thev=1→v=0 (v is the vibrational level quantum number designator) linesfrom an HBr chemical laser were used to pump a low-pressure mixture ofHBr and CO₂ gases. Vibrational energy transfer from HBr followed by a9.6 μm stimulating pulse populated the CO₂ [10°0,02°0] level.

The primary deficiency is, as per the prior cited patents and article,the use of a Hydrogen Bromide laser pump which, in practice, is notsuitable. Chemical lasers, though in general efficient, require thehandling of exhaust product and precursor fuel and oxidizer. Even ifpurely cold-reaction discharge initiated by dissociation of a halogendonor, these are then typically inefficient and still require productgas handling. In addition, HBr is a multiline molecular laser with adefined emission line structure, thus at approximately atmosphericpressure or less the CO₂ attributable absorption line structure is onlyin sporadic proximity to a limited number of HBr lines, both CO₂ and HBrof limited bandwidth and thus efficient pump utilization is not easilyachieved under such conditions. That is to say, HBr is not continuouslytunable within a broad band, thus as a pump for CO₂ it offers, at low tomoderate pressure, no more than limited line matching. In addition, the1→0 transition of HBr occupies the spectral range 2400 cm⁻¹ to 2700cm⁻¹, which presents essentially no spectral overlap with the 00 ⁰ 0→00⁰ 1 CO₂ transition being pumped. The forgoing has direct implications inregards baseline useful (for any isotopologue of CO₂) emission from HBr,and thus global system efficiency whether or not CO₂ is at pressure.Further deficiencies, common to this cited prior art and those citedbelow are presented in the final paragraphs of this section.

The preceding approaches are all deficient relative to that of thisproposal by virtue of this proposal's specific utilization of laserdiode pumped Tm solid state as the source for the direct optical pumpingof CO₂, and derivative aspects thereof. Continuous tuning has beendemonstrated from ˜1.74 μm through ˜2.017 μm, which well matches the CO₂pump transition (00 ⁰ 0→20 ⁰ 1) range of ˜1.949 μm to 2.035 μm inclusiveof all isotopologues. Laser diode pumped Tm solid state systems havedemonstrated impressive performance. Raised pressure operation of saidCO₂ systems would render locking of Tm system spectral output onpressure broadened 00⁰0→20⁰1 transition technically simple. It has beenargued that use of optical pumping of molecular transitions necessarilyresults in reduced performance from the pump source system because ofneed to narrow the line width of these sources to match the line widthof the molecular transition concerned. This in turn depressing globalsystem performance. In the case of high pressure CO₂ the pumptransition, 00⁰0→20⁰1, coalesces into a band of width ˜1000 GHz to 2000GHz (or 12 to 24 nm) per isotopologue courtesy of pressure broadening at5 atms for example. Thus in this case this objection does not apply.Secondly, at high dopant level concentrations cross relaxation in Tmmedia is rapid and the pump pulse event duration required is typicallyin the region of ˜200 ns full width half maximum which is substantial,and finally it is possible to amplify several spectrally separatedwavelength components in a medium which has inhomogeneous linebroadening character, thus enhancing effective interaction bandwidth andthus system performance. This aspect is consistent with the onemethodology presented here of common amplification of a number of linesfor pumping of distinct isotopologues—or a unitary isotopologue onmultiple rotational vibrational transitions of the 00⁰0→20⁰1 combinationband.

The preceding approaches are deficient in that they do not identify thatone of the probable metastable levels likely to be populated post andduring the optical pump of the 20⁰1 band is the 01¹1 level of similarlifetime to the 00⁰1 level. Lasing from this level on the transition(s)01¹1→11¹0 and 01¹1→03¹0 will display twice as many lines as to be foundin the traditional 00⁰1→10⁰0 and 00⁰1→02⁰0 transition(s)—this a resultof elimination of double degeneracy present for zero angular momentumcase, and resulting in continuous tunability of system at half thepressure required for zero angular momentum excited level CO₂.

The preceding approaches are deficient in that optically pumped raisedpressure multi CO₂ isotopologue, symmetric and asymmetric, gas mixoperation is not identified as a solution to the specific applicationsof remote sensing and sub picosecond pulse amplification courtesy of theimpressively broad, and reproducible, spectrally contiguous gainspectrum resulting therefrom. This enhanced by probable 01 ¹ 1metastable contribution under appropriate conditions. Optical pumpinghas the added benefit, if applied appropriately, of not drivingsignificant dissociation in gas and thus can preserve and sustainpredefined gas premixes.

Traditional discharge, radio frequency (RF) or e-beam pumping isdeficient for a number of interrelated issues. Firstly, they aregenerally associated with dissociation of the gas mix, and thus requirecatalyzers for gas recovery. In the case of RF it is restricted to lowpressure CO₂ operation and is thus only sensible within the ContinuousWave (CW) or quasi CW operational regime. Real gain switchedenergy/power is not feasible. In the case of high pressure operationonly transverse discharge or e-beam applications are sensible in anyway; however the discharge voltage, switching requirements and pulseforming network strictures render this difficult and impractical in mostapplications and reliability is typically a serious issue. This kind ofhigh voltage/high current switching also carries with it the requirementfor high voltage supplies and electro magnetic interference (EMI), whichare derived from the high voltage/high current discharge events.

SUMMARY OF THE INVENTION

The present invention and its enabling feature is a laser diode excited,Thulium (Tm) doped solid state system directly optically pumping the00⁰0→20⁰1 combination band transition of CO₂. The Tm doped solid statesystem may be pulsed or Continuous Wave (CW). CO₂ is the gas lasingmaterial. As at the primary electrical interface the system is laserdiode pumped the electronic system issues are low voltage and switching.Low voltage is easily and efficiently switched even at high currents.Given the optically pump enabled sustainability of multi CO₂isotopologue (symmetric and asymmetric) active gas mixes this wouldadmit, at raised pressure, a system with continuously tunable outputfrom ˜9 μm to ˜11.5 μm (indeed to ˜12 μm given the 01¹1→11¹0transition). CW or pulsed operation is permitted (FIG. 1 and FIG. 2).The laser diode pumped Tm solid state system is spectrally ideallymatched to the 00⁰0→20⁰1 CO₂ transition. Those CO₂ isotopologues notdirectly pumped would be collisionally pumped by rapid near resonant

excitation exchange interactions. Matching of pump mode volume to thatof CO₂ mode volume will optimize efficiency and maximize volumetricextraction feasible. Catalyzer free system operation under appropriatepump conditions is expected.

It is therefore the object of the present invention to provide adirectly optically pumped ˜9 μm to ˜11.5 μm CO₂ laser (amplifier)concept which overcomes the shortcomings of prior art devices and makesit practical to use in remote sensing and sub picosecond pulseamplification applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, illustrate embodiments of the invention and, togetherwith the description, serve to explain the principles of the invention.

FIG. 1: Is an illustration of the pulsed manifestation of the invention.One or more synchronized pulsed oscillators, individually tuned andlocked onto selected CO₂ isotopologue(s) pump transitions (00⁰→20⁰1)(A). Output via spectral beam combiner (B) (or any other beam combinerif required) into amplifier (C). Amplifier output via spectral beamcombiner (or dichroic optics) to admit introduction to CO₂ laser cavity(D) with −10 μm output (E).

FIG. 2: Is an illustration of the CW manifestation of the invention. Oneor more CW or synchronized quasi CW fiber oscillators, tuned and lockedindividually to selected CO₂ isotopologue(s) pump transitions(00⁰0→20⁰1) (A). Output via suitable beam combiner (B) into fiberamplifier (C). Amplifier output, via suitable beam combiner or dichroicoptics, into CO₂ laser cavity (D) with ˜10 μm output (E).

FIG. 3: Is an example of an induced multi-isotopologue gain spectrum at5 atms for an arbitrary pre-mix. This, excluding transitioncontributions from the anticipated 01¹1 metastable level which wouldserve to smooth and further broaden the gain spectrum.

DETAILED DESCRIPTION OF INVENTION

Laser diode excited Thulium (Tm) doped solid state system component(FIG. 1.A, B, C & FIG. 2.A, B, C). Both pulsed and continuous wave (CW)operation is feasible. In pulsed case extractions of ˜4 kJ/liter isachievable, enabling a compact related system. Ceramic host structureshave been formed, admitting arbitrary shaping and sizing of Tm:host(host being any suitable glass or crystalline host) and thusenergy/power scaling. Operation is quasi 4 level, thus pulsedefficiency, optical out to optical absorbed, in excess of 40% is inprinciple achievable. In CW case, slope efficiencies approaching 80% isfeasible, with single frequency operation at ˜1 kW, without anyindication of onset of stimulated Brillouin scattering limiting. Tuningspectral range can extend from 1.74 μm to 2.017 μm. The CO₂ 00⁰0→20⁰1pump transitions for the isotopologues , ¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹²C¹⁸O₂,¹³C¹⁸O₂, ¹⁶O¹²C¹⁸O and ¹⁶O¹³C¹⁸O are found to spectrally range from˜1.949 μm to 2.035 μm. There is thus significant overlap and hence pumpaccess.

The laser diode excited Tm doped solid state optical pump approach toCO₂ is absent the high voltage switching, discharge electrode erosionand electromagnetic interference (EMI) issues of traditional pulsedischarge, significantly gain switched, CO₂ lasers. In addition, it canreadily access the high pressure CO₂ operational regime desirable incertain applications.

There are a variety of photonic and collisionally mediated interactionswhich have the capability of rapidly transitioning population from thepump terminal level to either, or both, the 00⁰1 and 01¹1 metastablelasing levels. The 01¹1 level presents with a strong Q branch transition(˜15.3 μm) to the 00⁰1 level should such be desirable. This may, bydesign be encouraged or discouraged. The non-zero angular momentummetastable level is desirable for specific applications as it presentswith twice the transition lines of the zero angular momentum case andthus will be continuously tunable at a pressure below that required forzero angular momentum metastable level.

Optical pumping, absent the significant dissociation and catalyzerdriven recombination as required in most competitive discharge pumpedCO₂ systems, admits arbitrary sustainable use of predetermined CO₂isotopologue mixes. For example, in a discharge driven system withcatalyzer one can use a mix of ¹²C¹⁶O₂+¹³C¹⁶O₂, but not of¹²C¹⁶O₂+¹²C¹⁸O₂ or ¹²C¹⁶O₂+¹³C¹⁸O₂, as mixture will in time corrupt to¹²C¹⁶O₂+¹²C¹⁸O₂+¹⁸O¹²C¹⁶O and ¹²C¹⁶O₂+¹³C¹⁸O₂+¹⁸C¹²C¹⁶O+¹⁸O¹³C¹⁶O. Inthe case of appropriate optical pumping, as indicated, a desirablearbitrary premix of these gases can be implemented and will be largelypreserved in use.

Continuous tunability deriving from an appropriate gas premix, pressureand optical pumping is expected for example then to present with asustainable gain spectral distribution of the form FIG. 3.

The following is a description of the best mode contemplated by theinventor of the laser diode excited solid state optically pumped CO₂system. A laser diode excited Tm solid state pulsed laser, frequency(s)locked on desired CO₂ isotopologue(s) combination band(s) (00⁰0→20⁰1)(FIG. 1.A, B, C), seed oscillators synchronized, output coupled as inputinto CO₂ cavity region and mode matched to related CO₂ cavity determinedlasing volume (FIG. 1.D). Laser plus amplifier combination possiblyamplifying more than one pump transition frequency as indicated in FIG.1A, B, C.

The following is a description of an alternate embodiment contemplatedby the inventor of the laser diode excited solid state optically pumpedCO₂ system. A laser diode excited Tm solid state CW laser, frequency(s)locked on desired CO₂ isotopologue(s) combination band(s) (00⁰0→20⁰1)(FIG. 2.A, B, C), output coupled as input into CO₂ cavity region andmode matched to related CO₂ cavity determined lasing volume (FIG. 2.D).Laser plus amplifier combination possibly amplifying more than one pumptransition frequency as indicated in FIG. 2.A, B, C.

At high pressure, 00⁰0→20⁰1 pump transition bandwidth is sufficientlylarge to admit sufficiently broad solid state system bandwidth forefficient operation. At reduced pressure and for pump events underseveral hundred nanoseconds, for a single CO₂ isotopologue pumped onseveral selected rotational vibrational lines of the 00⁰0→20⁰1transition, the interaction will yield adequate solid state interactionbandwidth for efficient operation. Similarly at reduced pressure butwith several CO₂ isotopologues pumped on selected rotational vibrationaltransitions of their respective 00⁰0→20⁰1 transitions the solid stateinteraction bandwidth will be adequate for efficient operation.

Coupling, or combination, of ˜2 μm with ˜10 μm cavity axis and modevolume via either dispersion in prisms or dichroic optics (FIG. 1.D &FIG. 2.D). Prisms cut with apex angle such that surface interactions areon Brewster angle for CO₂ wavelength range, and near Brewster for ˜2 μmpump. Prism material ideally low index as such typically reduces lossesattributable to slight angular offsets.

Single or multi CO₂ isotopologue gas mix situations are equallydesirable from a system standpoint. Selection of gas mix and pressure tobe utilized a function of intended application; high pressure andcontinuously tunable, near atmospheric or modest sub atmospheric andline tunable.

In pulsed high power optically pumped applications significantly subatmospheric pressure not desirable as due to notably reduced relaxationrates alternate high gain transitions are not suppressed by excitationrelaxation into the 00⁰1 and 01¹1 levels, other than should thosespecific transitions be desired which amongst others include a band from4.2 μm to 4.3 μm and a structure at ˜15.26 μm. In some of the lattercases a resonant cavity is not necessarily required as gain issufficiently high to result in amplified spontaneous emission.

Utilization of atmospheric, or higher, pressure non pumped low gain CO₂gas cells intra cavity (FIG. 1.D & FIG. 2.D) if required to suppress˜4.2 μm to 4.3 μm and ˜15.26 μm transitions is permitted. Low gaindenotes spectrally selective absorption.

In a multi isotopologue gas mix, pumping of several isotopologues ispreferable to pumping only one. At significant pressure this is lessrelevant as rate of cross relaxation to neighboring isotopologuesincreases.

Gas flow for thermal management at power, in reduced power applicationsdiffusion cooling to waveguide or containment structure acceptable.

CO₂ cavity optics commensurate with intended application. Tunable ifcontinuous or line tunability required, otherwise simple broadband (FIG.1.D & FIG. 2.D).

Intra CO₂ cavity preferred use of transmitting optics (windows) atBrewster angle as this is favorable from a surface fluence reductionstandpoint, plus minimizes Fresnel losses at ˜2 μm and ˜10 μm withoutneed for dual wavelength anti reflection coatings (FIG. 1.D & FIG. 2.D).

The CO₂ component isotopologue(s) may be admixed with at least one, ormore, buffer gases selected from the group consisting of Helium, Argonand Nitrogen.

This laser diode excited, solid state pumped CO₂ presents with a numberof capabilities deriving from its particular features. Specifically, itis well suited to remote sensing applications requiring line orcontinuous tunability from ˜9 μm through and above 11.5 μm. Similarly,at pressure, it is suited to utilization as a broadband amplifier forsub picosecond pulse amplification and for high energy high powerpulsed, or other applications requiring high energy pulsed output,disruption of thermal imaging systems of various types. Finally,utilization as a simple non tuned pulsed laser for industrialapplications benefits from the methodologies general non dependence onan internal catalyzer for any meaningful gas lifetime.

The forgoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in the light of the aboveteaching. The embodiments disclosed were meant only to explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best use the invention in variousembodiments and with various modifications suited to the particular usecontemplated.

1. An optically pumped CO₂ laser comprising, at least, a laser diodeexcited Tm solid state laser tuned to the 00⁰0→20⁰1 combination bandtransition(s) of the CO₂ isotopologue(s) to be optically pumped forlasing purposes; gas cell with desired CO₂ gas mix and pressure internalto a resonant cavity and pump field and CO₂ cavity axis combinationmethodology; CO₂ lases in atmospherically transmissive window withinspectral region from ˜9 μm to ˜11.5 μm.
 2. An optically pumped CO₂laser, according to claim 1, wherein if the optically pumped CO₂ is atpressure, laser diode pumped solid state system efficiency is notlimited by molecular line widths and more relaxed conditions apply; atreduced pressure where molecular lines resolve individually multiplerotational vibrational transitions may be pumped thus broadening solidstate system interaction bandwidth sufficiently for efficientextraction, achievable with single or multi isotopologue gas mix.
 3. Anoptically pumped CO₂ laser, according to claim 1, wherein the opticallypumped CO₂ metastable levels accessible for defined ˜9 μm to ˜11.5 μmlasing include the 00⁰1 and 01¹1 levels.
 4. An optically pumped CO₂laser, according to claim 1, wherein the Tm solid state pump laser maybe CW or pulsed and thus the optically pumped CO₂ lasing may be CW orpulsed.
 5. An optically pumped CO₂ laser, according to claim 1, whereinthe CO₂ component is optically pumped and thus, above atmosphere tosignificantly above atmosphere operation is straightforward other thanfor pressure containment considerations.
 6. An optically pumped CO₂laser, according to claim 1, wherein the CO₂ component admitsutilization of atmospheric, or higher, pressure non pumped low gain gascells intra cavity to suppress ˜4.2 μm to 4.3 μm and ˜15.26 μmtransitions if desired or required.
 7. An optically pumped CO₂ laser,according to claim 1, wherein the CO₂ component, which absentdissociation and discharge related gas contamination under appropriateoptical pump conditions, results in near indefinite gas lifetimes.
 8. Anoptically pumped CO₂ laser, according to claim 1, wherein in the absenceof dissociation a catalyzer is not a system requirement.
 9. An opticallypumped CO₂ laser, according to claim 1, wherein given a laser diodeexcited Tm solid state pump, then fact that ceramic Tm:YAG has beenformed and thus in principle arbitrarily large and shaped Tm:YAGstructures can be fabricated in conjunction with a demonstrated ˜4kJ/liter extraction, coupled with the inherent volume scalability of theoptically pumped gas component allows for high energy pulsedapplications with output in the ˜9 μm to ˜11.5 μm band; YAG isreferenced, but any other suitable solid state host is acceptable. 10.An optically pumped CO₂ laser, according to claim 1, wherein the CO₂component isotopologue(s) may be admixed with one, or more buffer gasesselected from the group consisting of Helium, Argon and Nitrogen.
 11. Anoptically pumped CO₂ laser, according to claim 1, wherein the laserdiode excited Tm doped solid state optically pumped molecular CO₂approach is absent chemical reaction sourced optical pumping, and thusis absent related precursor or product gas handling issues plus anyefficiency shortfall attributable to line mismatches
 12. An opticallypumped CO₂ laser comprising sustained and preserved multi-CO₂isotopologue, symmetric and asymmetric, mix capability courtesy ofabsence of significant optical pump driven dissociation underappropriate conditions.
 13. An optically pumped CO₂ laser according toclaim 12, wherein the CO₂ component ,which absent dissociation, admitsutilization of an arbitrarily proportioned multi isotopologue CO₂ gasmix offering optimal line tunability from ˜9 μm through ˜11.5 μm atmoderate pressure and continuous tunability from ˜9 μm through ˜11.5 μmat high pressure.
 14. An optically pumped CO₂ laser, according to claim12, wherein the CO₂ component admits utilization of atmospheric, orhigher, pressure non pumped low gain gas cells intra cavity to suppress˜4.2 μm to 4.3 μm and ˜15.26 μm transitions if desired or required. 15.An optically pumped CO₂ laser, according to claim 12, wherein givenspectral tunability a system well suited to remote sensing of agents ofinterest is enabled.
 16. An optically pumped CO₂ laser, according toclaim 12, wherein at pressure a system is enabled which is suitable foruse for short pulse amplification of ˜10 μm CO₂ laser events into thesub picosecond timescale (FIG. 3), or for compact high energy pulsedextraction.
 17. An optically pumped CO₂ laser, according to claim 12,wherein as a result of the feasibility of utilization of asymmetricisotopologues and/or the 01¹1 excited level the system pressure requiredfor continuous tunability will be 50% or less than that required for thepurely symmetric isotopologues.
 18. An optically pumped CO₂ laser,according to claim 12, wherein absent dissociation, a catalyzer is not asystem requirement.
 19. An optically pumped CO₂ laser comprising a laserdiode excited Tm doped solid state optical pump wherein the approach toCO₂ is absent the high voltage switching, discharge electrode erosionand EMI issues of traditional pulse discharge (significantly gainswitched) CO₂ lasers.
 20. An optically pumped CO₂ laser, according toclaim 19, wherein absent high voltage high energy switching and highdischarge current related electrode erosion, system mean time betweenrequired services will be extended.